As discussed previously, in order to have the two-loop neutrino masses in our model, the non-zero coupling constants \(\lambda _5\)  and \(\kappa \)  are both required. The former splits the masses between \(H^0\)  and \(A^0\) , and the latter mixes the charged states \(\chi ^\pm \)  and \(s^\pm \)  which carry different EW gauge quantum numbers. Both effects could change the values of the EW oblique \(S\)  and \(T\)  parameters. In particular, the \(T\)  parameter should yield a stronger constraint on this model.
The deviation of \(T\)  from the SM is given by [1]}
\(\Delta T&=&{1\over 4\pi s_W^2 M_W^2}\Big [{s_\theta ^2\over 4}(F_{S_1^\pm ,H^0}+F_{S_1^\pm ,A^0})+{c_\theta ^2\over 4}(F_{S_2^\pm ,H^0}+F_{S_2^\pm ,A^0})-{1\over 2}c_\theta ^2 s_\theta ^2F_{S_1^\pm ,S_2^\pm }-{1\over 4}F_{H^0,A^0}\Big ]\;,\nonumber \\\) 
